1. Field of the Invention
The present invention relates to a method of preparing a transparent polymer material comprising a thermoplastic polycarbonate and nanoparticles, as well as to a transparent polymer material obtained by said method.
The invention typically applies, but not exclusively, to the fields of optics, in particular to optical articles of the aiming instrumentation lens type, helmet visor type, or ophthalmic lens type, and to optical articles of the automobile glass type.
More particularly, the term “ophthalmic lens” means lenses that are in particular suitable for mounting in eyeglasses, having the function of protecting the eye and/or correcting vision, such lenses being selected from afocal, single-vision, bifocal, trifocal and progressive lenses.
More particularly, the term “automobile glass” not only means external transparent bodywork elements such as rear lights, side panels, side windows, glazed roofs, headlight or sidelight glazing, but also transparent elements for the interior, such as dashboard, dial, or screen glazing.
2. Description of Related Art
Polycarbonate enjoys advantages that render it particularly advantageous for optics, in particular excellent transparency, excellent resistance to impacts, a high refractive index, and being very lightweight. In contrast, its principal disadvantages lie in it not being very rigid and being sensitive to scratching and abrasion.
In order to improve the mechanical properties of a polymer, in particular its rigidity and its abrasion and scratch resistance, it is known to add mineral nanoparticles to the polymer. Typically, said mineral nanoparticles are incorporated directly into the polymer in the molten state. However, that process applied to a thermoplastic polycarbonate does not guarantee good dispersion of the nanoparticles in the thermoplastic polycarbonate matrix and frequently results in degradation of said matrix.
The material obtained thereby is thus less transparent and less impact resistant compared with a thermoplastic polycarbonate material including no nanoparticles.